Reliable metal bumps on top of I/O pads after removal of test probe marks

ABSTRACT

In accordance with the objectives of the invention a new method is provided for the creation of metal bumps over surfaces of I/O pads. Contact pads are provided over the surface of a layer of dielectric. The aluminum of the I/O pads, which have been used as I/O pads during wafer level semiconductor device testing, is completely or partially removed over a surface area that is smaller than the surface area of the contact pad using methods of metal dry etching or wet etching. The contact pad can be accessed either by interconnect metal created in a plane of the contact pad or by via that are provided through the layer of dielectric over which the contact pad has been deposited. The process can be further extended by the deposition, patterning and etching of a layer of polyimide over the layer of passivation that serves to protect the contact pad.

This application is related to attorney docket number MEG01-001, filedon ______, Ser. No. ______, assigned to a common assignee.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to the fabrication of integrated circuit devices,and more particularly, to a method of removing damage to I/O pads thathave been repetitively contacted and possibly damaged by test probes,thereby avoiding potential solder bump reliability problems.

(2) Description of the Prior Art

In creating semiconductor devices, the technology of interconnectingdevices and device features is a continuing challenge in the era ofsub-micron devices. Bond pads are frequently used for this purpose,whereby continuous effort is dedicated to creating bond pads that aresimple, reliable and inexpensive.

Bond pads are generally used to wire device elements and to provideexposed contact regions of the die. These contact regions are suitablefor wiring the die to components that are external to the die. Anexample is where a bond wire is attached to a bond pad of asemiconductor die at one end and to a portion of a Printed Circuit Boardat the other end of the wire. The art is constantly striving to achieveimprovements in the creation of bond pads that simplify themanufacturing process while enhancing bond pad reliability.

A frequently used bond pad consists of an exposed aluminum pad. A goldbond wire can be bonded to this aluminum pad. Materials that aretypically used for bond pads include metallic materials, such astungsten and aluminum, while heavily doped polysilicon can also be usedfor contacting material. The bond pad is formed on the top surface ofthe semiconductor device whereby the electrically conducting material isfrequently embedded in an insulating layer of dielectric.

Contact pads, having dimensions of between about 40×40 μm and 120×120μm, are in current practice frequently used as access or input/outputcontact points during wafer level testing of semiconductor devices. Inview of the complexity and density of high performance semiconductordevices, these contact pads will, during a complete cycle of testing, becontacted a number of times. Testing is, as a matter of economicnecessity, performed at high speed, which frequently results in landingthe test probe on the surface of the contact pad at high speed,resulting in mechanical damage (in the form of probe marks) to thesurface of the contact pad. Especially for memory products, a wafer istested at least two times, that is before and after repair of faulty(weak or bad) memory lines. The distribution of the location of theprobe mark over the surface of the contact pad is, in a well controlledtesting production line, limited to a surface area of about 60×60 μm.Surface damage to the contact pad may occur in the form of a dent (inthe surface of the contact pad) or may even become severe enough thatthe surface of the contact pad is disrupted, resulting in the occurrenceof burring in the surface of the contact pad. After the contact padshave in this manner been used as an I/O point for accessing thesemiconductor device during high speed testing, a number of thesecontact pads are frequently used for the creation of solder bumps orgold bumps over the surface thereof. In instances where the surface ofthe contact pad is damaged, it is clear that the surface of the contactpad forms a poor basis on which to create a solder bump or a gold bump.The invention addresses this concern and provides a method wherebysurface damage to contact pads is removed.

U.S. Pat. No. 6,162,652 (Dass et al.) provides for the testing of anintegrated circuit device including depositing a solder bump on asurface of a bond pad.

U.S. Pat. No. 5,756,370 (Farnworth et al.) provides a compliant contactsystem for making temporary connection with a semiconductor die fortesting and a method for fabricating the pliable contact system.

U.S. Pat. No. 5,554,940 (Hubacker) addresses the probing ofsemiconductor devices that have been provided with contact bumps and theformation of peripheral test pads.

SUMMARY OF THE INVENTION

A principle objective of the invention is to eliminate the effect ofsurface damage to I/O pads that has been caused by using these I/O padsas contact points for wafer level testing of semiconductor devices.

Another objective of the invention is to eliminate the effect of probemarks on the surface of I/O pads for I/O pads that have been used ascontact points for wafer level testing of semiconductor devices.

In accordance with the objectives of the invention a new method isprovided for the creation of metal bumps over surfaces of I/O pads.Contact pads are provided over the surface of a layer of dielectric. Thealuminum of the I/O pads, which have been used as I/O pads during waferlevel semiconductor device testing, is completely or partially removedover a surface area that is equal to or smaller than the surface area ofthe contact pad using methods of metal dry etching or wet etching. Thecontact pad can be accessed either by interconnect metal created in aplane of the contact pad or by vias that are provided through the layerof dielectric over which the contact pad has been deposited. The processcan be further extended by the deposition, patterning and etching of alayer of polyimide over the layer of passivation that serves to protectthe contact pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b show a top view and a cross section of a prior artmetal bump that is created over the surface of an aluminum pad that hasbeen used as an I/O contact pad during wafer level device testing.

FIGS. 2 a through 2 d show a top view and a cross section of theimplementation of the first embodiment of the invention, that is thecontact pad is completely or partially etched within the opening thathas been created in the protective layer of passivation. The contact padis contacted by means of interconnect metal (not shown) that has beencreated in the plane of the contact pad, the interconnect metal is notpart of the invention.

FIGS. 3 a through 3 d show a top view and a cross section of theimplementation of the second embodiment of the invention, that is thecontact pad is completely or partially etched. The contact pad iscontacted by means of an array of vias created in the underlying layerof dielectric, this array of vias is not part of the process of theinvention.

FIGS. 4 a through 4 d show a top view and a cross section of theimplementation of the third embodiment of the invention. A layer ofpolyimide has been added to the structure, the contact pad is completelyor partially etched within the opening that has been created in thelayer of polyimide. The contact pad is contacted by means ofinterconnect metal (not shown) that has been created in the plane of thecontact pad, the interconnect metal is not part of the invention.

FIGS. 5 a through 5 d show a top view and a cross section of theimplementation of the fourth embodiment of the invention. A layer ofpolyimide has been added to the structure, the contact pad is completelyor partially etched. The contact pad is contacted by means of an arrayof vias created in the underlying layer of dielectric, this array ofvias is not part of the process of the invention.

FIGS. 6 through 13 b address the processing steps of the inventionwhereby no layer of polyimide is used, as follows:

FIG. 6 shows a cross section of a semiconductor surface, a layer ofdielectric has been deposited over the semiconductor surface, a contactpad has been provided over a layer of dielectric. A layer of passivationhas been deposited, patterned and etched, creating in opening in thelayer of passivation that aligns with the contact pad. A probe mark ishighlighted.

FIG. 7 shows a cross section after the contact pad has been partiallyetched using the layer of passivation as a self-aligned etching mask.The contact pad is contacted by means of interconnect metal (not shown)that has been created in the plane of the contact pad, the interconnectmetal is not part of the invention.

FIG. 8 shows a cross section after the contact pad has been partiallyetched using the layer of passivation as a self-aligned etching mask.The contact pad is contacted by means of an array of vias created in theunderlying layer of dielectric, this array of vias is not part of theprocess of the invention.

FIG. 9 a shows a cross section after the contact pad has been completelyetched using the layer of passivation as a self-aligned etching mask.The contact pad is contacted by means of interconnect metal (not shown)that has been created in the plane of the contact pad, the interconnectmetal is not part of the invention.

FIG. 9 b shows a cross section after the contact pad has been completelyetched using the layer of passivation as a self-aligned etching mask.The contact pad is contacted by means of an array of vias created in theunderlying layer of dielectric, this array of vias is not part of theprocess of the invention.

FIG. 10 a shows a cross section after a layer of UBM has been formedoverlying the partially etched contact pad and the layer of passivationof FIG. 7.

FIG. 10 b shows a cross section after a layer of UBM has been formedoverlying the partially etched contact pads and the layer ofpassivation. The contact pad is contacted by means of an array of viascreated in the underlying layer of dielectric, this array of vias is notpart of the process of the invention.

FIG. 11 a shows a cross section after a layer of photoresist has beendeposited, patterned and etched over the structure of FIG. 10 a,creating an opening in the layer of photoresist that aligns with thecontact pad. A layer of enhanced UBM has been deposited over the surfaceof the layer of UBM.

FIG. 11 b shows a cross section after a layer of photoresist has beendeposited, patterned and etched over the structure of FIG. 10 b,creating an opening in the layer of photoresist that aligns with thecontact pad. A layer of enhanced UBM has been deposited over the surfaceof the layer of UBM.

FIG. 12 a shows a cross section after a layer of bump metal has beendeposited over the layer of enhanced UBM of the structure of FIG. 11 a.

FIG. 12 b shows a cross section after a layer of bump metal has beendeposited over the layer of enhanced UBM of the structure of FIG. 11 b.

FIG. 13 a shows a cross section after photoresist stripping and etchingof the layer of UBM of the structure of FIG. 12 a.

FIG. 13 b shows a cross section after photoresist stripping and etchingof the layer of UBM of the structure of FIG. 12 b.

FIGS. 14 a through 18 b address the processing steps of the inventionwhereby a layer of polyimide is used, as follows:

FIG. 14 a can be compared with FIG. 7, a layer of polyimide has beenadded and patterned to the cross section that is shown in FIG. 14 a. Thecontact pad is then either partially or completely etched in accordancewith the opening created in the layer of polyimide.

FIG. 14 b can be compared with FIG. 8. A layer of polyimide has beenadded and patterned to the cross section that is shown in FIG. 14 b. Thecontact pad is then either partially or completely etched in accordancewith the opening created in the layer of polyimide.

FIG. 15 a can be compared with FIG. 10 a, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 15 a.

FIG. 15 b can be compared with FIG. 10 b, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 15 b.

FIG. 16 a can be compared with FIG. 11 a, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 16 a.

FIG. 16 b can be compared with FIG. 11 b, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 16 b.

FIG. 17 a can be compared with FIG. 12 a, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 17 a.

FIG. 17 b can be compared with FIG. 12 b, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 17 b.

FIG. 18 a can be compared with FIG. 13 a, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 18 a.

FIG. 18 b can be compared with FIG. 13 b, a patterned layer of polyimidehas been added to the cross section that is shown in FIG. 18 b.

FIGS. 19 a through 19 c show prior art methods of creating a contactpad, the contact pad is contacted by means of interconnect metal that iscreated in the plane of the contact pad.

FIGS. 20 a through 20 d show prior art methods of creating a contactpad, the contact pad is contacted by means of vias that penetrate thelayer of dielectric over which the contact pad is deposited.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Contact pads, having dimensions of about between about 60×60 μm and120×120 μm, are in current practice frequently used as access orinput/output contact points during wafer level testing of semiconductordevices. In view of the complexity and density of high performancesemiconductor devices, these contact pads will, during a complete cycleof testing, by contacted a number of times. Testing is as a matter ofeconomic necessity performed at high speed which frequently results inlanding the test probe on the surface of the contact pad at high speed,resulting in mechanical damage to the surface of the contact pad. In awell controlled testing production line, the distribution of the probemarks (or the damaged surface area of the contact pad) is limited(controlled) to an area in the range of about 60×60 μm. This surface mayoccur in the form of a dent in the surface of the contact pad or mayeven become severe enough that the surface of the contact pad is brokenresulting in the occurrence of burring in the surface of the contactpad. After the contact pads have in this manner been used as I/O pointsduring high speed testing, a number of these contact pads are frequentlyused for the creation of solder or gold bumps over the surface thereof.In instances where the surface of the contact pad is damaged, it isclear that the surface of the contact pad forms a poor basis on which tocreate a solder bump or a gold bump. The invention addresses thisconcern and provides a method whereby surface damage to contact pads isremoved.

For memory products, such as SRAM devices, probe testing which uses bondpads for accessing the devices, must be performed prior to creatingwafer solder bumps on the surface of the bond pads, this in order toallow for memory repairs of faulty devices. The most recent practice isfor the repair of memory products to be performed by opening (breakingor interrupting) polysilicon fuses using lasers. As indicated above, thetesting can cause damage to the surface of the bond pads, creatingproblems of solder bump and device reliability.

This is further highlighted in FIGS. 1 a and 1 b. FIG. 1 a shows a topview of a metal bump structure that is created using current practices.FIG. 1 b shows a cross section of the metal bump structure using currentpractices. It is assumed that the views that are shown in FIGS. 1 a and1 b relate to an aluminum contact pad that has been used as a point ofI/O for testing of a device at the wafer level, using a tester probe tocontact the aluminum pad.

Shown in FIG. 1 a is a top view of a prior art metal bump having thefollowing elements:

-   -   24, an aluminum contact pad    -   25, the circumference of a metal bump overlying aluminum contact        pad 24    -   27, the circumference of the opening created in the protective        layer 32 of passivation (see FIG. 1 b)    -   28, a probe mark caused by a tester probe (not shown) in the        surface of aluminum contact pad 24.

Shown in FIG. 1 b is a cross section of a prior art metal bump havingthe following elements:

-   -   10, the silicon substrate over which the aluminum contact pad        has been created    -   24, an aluminum contact pad    -   28, the probe mark or bump that has been created in the surface        of the aluminum contact pad 24 by the tester probe (not shown)    -   29, a layer of dielectric that has been deposited over the        surface of substrate 10;    -   32, a layer of passivation that has been deposited over the        surface of the layer 29 of dielectric; an opening (with a        circumference 27, as shown in FIG. 1 a) has been created in the        layer 32 of passivation    -   33, a layer of under-bump-metal (UBM) overlying the aluminum pad        24    -   20, a layer of metal, such as copper or nickel, that forms an        integral part of the pedestal of the metal bump    -   35, the metal bump created overlying the aluminum contact pad        24.

From the above it must be understood that, after the testing has beencompleted, the layer 33 of under bump metal is created overlying thealuminum contact pad 24. The surface of aluminum contact pad 24 is notplanar (as shown with the probe mark 28 in FIG. 1 b) and is in manyinstances disturbed in an unpredictable manner by the tester probe. Thelayer 33 of under bump metal does therefore in most cases not fill thedamaged surface region 28 of the aluminum pad 24. This opens thepotential for trapping foreign and undesirable materials, such asmoisture, a processing gas, a plating solution, solvent and the like, inthe unfilled (by the layer 33 of under bump metal) regions in orsurrounding the probe mark 28 on the surface of the aluminum pad 24.

The invention addresses the above detailed problems that are encounteredin contact pads by providing the following solutions:

-   1) a contact pad of standard design, etching the contact pad and    completely or partially removing the aluminum of the contact pad    over a surface area of the contact pad that is bounded by the    opening that is created in the overlying protective layer of    passivation; the metal bump is created filling and overlying the    opening that has been created in the layer of passivation. The    contact pad is contacted by means of interconnect metal that is    created in the plane of the contact pad, this interconnect metal is    not part of the invention-   2) as highlighted under 1) above, in this case the contact pad is    contacted by means of one or more vias that are created penetrating    the layer of dielectric over the which the contact pad has been    deposited-   3) the design as indicated above under 1) whereby an extra layer of    polyimide has been added to the design of the contact bump; the    opening that is created in the layer of polyimide replaces the    previously used opening in the layer of passivation in providing the    boundaries for etching the contact pad. This layer of polyimide is    extremely important especially for memory products in applications    where fuse repair is required. The polyimide covers and protects    fuses during subsequent etching processes, such as for instance    contact pad etching-   4) the design as indicated above under 2) whereby an extra layer of    polyimide has been added to the design of the contact bump; the    opening that is created in the layer of polyimide replaces the    previously used opening in the layer of passivation in providing the    boundaries for etching the contact pad. The layer of polyimide can    similarly cover and protect fuses during etching in subsequent    processing steps.

These four highlighted approaches are further shown in FIGS. 2 a through5 d.

FIG. 2 a shows a top view of the metal bump of the invention thatapplies to the first embodiment of the invention. The contact pad 24 iscontacted by means of interconnect metal (not shown) that is created inthe plane of the contact pad and overlying the surface of layer 29 ofdielectric. Shown in FIG. 2 a are:

-   -   24, an aluminum contact pad    -   25, the circumference of a metal bump created overlying aluminum        contact pad 24    -   27, the circumference of the opening that is created in an        overlying protective layer 32 of passivation, see FIG. 2 b    -   28, the region in the surface of the aluminum contact pad 24        where a probe mark has been left by the tester probe.

It must be noted that the region that is bordered by circumference 27,FIG. 2 a, is the region of the contact pad 24 that is exposed andsurrounded by the layer 32 of passivation (FIG. 2 b). This surfaceregion is therefore the exposed surface of the contact pad 24 at thetime prior to the creation of Under Bump Metal over the surface of thecontact pad 24.

Shown in FIG. 2 b are:

-   -   10, the silicon substrate over which the aluminum contact pad        has been created    -   24, an aluminum contact pad    -   29, a layer of dielectric deposited over the surface of        substrate 10;    -   32, a layer of passivation deposited over the surface of the        layer 29 of dielectric; an opening has been created in the layer        32 of passivation    -   33, a layer of under-bump-metal (UBM) overlying the aluminum pad        24    -   34, a layer of enhanced UBM that forms an integral part of the        pedestal of the metal bump; layer 34 serves to enhance adhesion        between overlying layers, as a diffusion barrier and to form one        of the plates during the process of electroplating    -   35, the metal bump created overlying the aluminum contact pad        24.

It must be understood that the layer 32 of passivation that is depositedover the surface of said semiconductor surface can comprise a pluralityof layers of passivation material.

Notable in the cross section that is shown in FIG. 2 b is that thethickness of the contact pad 24 has been reduced by a considerableamount over a surface region of the contact pad 24 that is bordered bycircumference 27 (FIG. 2 a) of the layer 32 of passivation. As shown inthe cross section of FIG. 2 b, the contact pad has been reduced to athickness of about 2000 Angstrom. As one of the solutions to the problemof the probe bump in the surface of the contact pad, the contact pad canalso be completely removed within the opening of the layer 32 ofpassivation, down to the surface of the layer 29 of dielectric. Thislatter solution has been highlighted in the cross sections that areshown in FIGS. 2 c and 2 d where the contact pad has been etched down tothe surface of the layer 29 of dielectric.

FIGS. 3 a through 3 d show the solution of the invention whereby thecontact pad 24 is contacted by means of an array of vias 11 created inthe underlying layer 29 of dielectric. The creation of vias 11 is notpart of the invention. As in the solution that is shown in FIGS. 2 athrough 2 d, the contact pad can be reduced to a thickness of about 2000Angstrom (FIG. 3 b) or the contact pad can be etched down to the surfaceof the underlying layer 29 of dielectric (FIG. 3 d).

FIG. 4 a shows a top view of the metal bump that is essentially the sameas the cross section that is shown in FIG. 2 a with the addition of theline 46 which is the circumference of the opening that has been createdin a layer 40 (see FIG. 4 b) of polyimide that has been added to thestructure. FIGS. 4 a through 4 d address the case where the contact pad24 is contacted by means of interconnect metal (not shown) that iscreated in the plane of the contact pad and overlying layer 29 ofdielectric. Layer 40 of polyimide is better visible in the cross sectionthat is shown in FIG. 4 b. FIG. 4 b shows a cross section that isessentially the same as the cross section that is shown in FIG. 2 b withthe addition of a layer 40 of polyimide. The surface of contact pad 24is exposed (surface area 44 of FIGS. 4 a and 4 b) within the boundariesof the line 46, this prior to the creation of UBM layers overlying thecontact pad 24. The aluminum of the contact pad 24 can be etched, aslimited by the opening 46 that has been created in the layer 40 ofpolyimide. The etch can either completely remove the aluminum of thecontact pad 24 from above the surface of layer 29 of dielectric (FIG. 4d) or can reduce that thickness of the contact pad 24 to where about2000 Angstrom of aluminum remains in place on the surface of layer 29 ofdielectric (FIG. 4 b).

As FIGS. 4 a through 4 d have been related to FIGS. 2 a through 4 b, socan FIGS. 5 a through 5 d can be related to FIGS. 3 a through 3 d. FIG.5 a shows a top view of the metal bump of the invention that isessentially the same as the top view that is shown in FIG. 3 a with theaddition of the line 46 which is the circumference of the opening in alayer 40 of polyimide that has been added to the structure. FIGS. 5 athrough 5 d address the case where the contact pad 24 is contacted bymeans of vias 11 that have been created penetrating the underlying layer29 of dielectric. The creation of vias 11 is not part of the invention.This layer 40 of polyimide is again better visible in the cross sectionthat is shown in FIG. 5 b. FIG. 5 b shows a cross section that isessentially the same as the cross section that is shown in FIG. 3 b withthe addition of a layer 40 of polyimide. The surface of contact pad 24is visible (exposed) as bounded by the line 46, this prior to thecreation of UBM layers overlying the contact pad 24. The aluminum of thecontact pad 24 can be etched, limited by the opening 46 that has beencreated in the layer 40 of polyimide. The etch can either completelyremove the aluminum of the contact pad 24 from above the surface oflayer 29 of dielectric or can reduce that thickness of the contact pad24 to where about 2000 Angstrom of aluminum remains in place on thesurface of layer 29 of dielectric.

It must be noted that the use of polyimide films as inter-leveldielectrics has been pursued as a technique for providing partialplanarization of a dielectric surface. For memory products, thepolyimide covers and protects the fuses, which are used for memoryrepair, during aluminum etching or during UBM etching in the process ofthe invention. Polyimides offer the following characteristics for suchapplications:

-   -   they produce surfaces in which the step heights of underlying        features are reduced, and step slopes are gentle and smooth.    -   they are available to fill small openings without producing the        voids that occur when low-temperature CVD oxide films are        deposited.    -   the cured polyimide films can tolerate temperatures of up to 500        degrees C. without degradation of their dielectric film        characteristics.    -   polyimide films have dielectric breakdowns, which are only        slightly lower than that of SiO₂.    -   the dielectric constant of polyimides is smaller than that of        silicon nitride and of SiO₂.    -   the process used to deposit and pattern polyimide films is        relatively simple.

To summarize the invention:

-   -   an aluminum contact pad is provided over the surface of a layer        of dielectric, the layer of dielectric has been deposited on a        semiconductor surface, typically the surface of a semiconductor        substrate; the creation of the contact pad is not part of the        invention    -   the surface of the aluminum pad is partially exposed, prior to        formation of overlying layers of UBM and bump metal, either        through an opening that is created in a layer of passivation        that has been deposited over the layer of dielectric or through        an opening that has been created in a layer of polyimide that        has been deposited over the surface of a layer of passivation    -   the partially exposed surface of the aluminum pad is etched,        either completely or partially removing the aluminum from above        the surface of the layer of dielectric    -   the contact pad can be contacted either by means of interconnect        metal (not part of the invention) that is created in the plane        of the contact pad and overlying the layer of dielectric above        which the contact pad is located or by means of vias (not part        of the invention) that are created through the layer of        dielectric above which the contact pad is located.

Prior art methods that are used to create a contact pad are furtherhighlighted in FIGS. 19 a and 19 b and in FIGS. 20 a through 20 d. Thesefigures also address methods that can be used for the interconnection ofthe contact pad. Although these methods of interconnection of contactpads are not part of the invention, a brief review of these methods atthis time is considered of value.

FIGS. 19 a through 19 c address the conventional processing sequencethat is used to create an aluminum bond pad.

The process starts with a semiconductor surface 10, FIG. 19 a, typicallythe surface of a silicon single crystalline substrate. Aninterconnection scheme 13′ consisting of one or more layers of metal andIntra Metal Dielectric (IMD) is created over the surface 10. A layer 17′of metal, typically aluminum, is deposited over the surface of the layer13′. Layer 17′ of aluminum is patterned and etched, typically using alayer of photoresist (not shown in FIG. 19 a) and conventional methodsof photolithography and etching. After the bond pad 17′, FIG. 19 b, hasbeen created in this manner, and after interconnect 19′ has beencreated, a layer 11′ of passivation is deposited over the layer 13′. Anopening 15′ that aligns with the bond pad 17′ is created in the layer11′ of passivation, again using methods of photolithography and etching.Shown in cross section in FIG. 19 b is element 19′, which represents onemethod of connecting the contact pad 17′ to surrounding circuitelements. FIG. 19 c shows a top view of the contact pad 17′, the topview of the contact pad 17′ that is shown in FIG. 19 c showsinterconnection 19′ (to other electrical components) and the opening 15′that is created in the layer 11′ of passivation. The contact pad that isshown in FIGS. 19 a through 19 c is accessed by means of interconnectmetal (19′) which is created in the plane of the contact pad 17′.

Another approach that is used to access a contact pad is shown in FIGS.20 a through 20 d. Using this approach, the contact pad 17′ is accessedby means of vias that are in contact with the contact pad. FIG. 20 ashows a top view of a contact pad 17′ that is exposed through opening15′ in a layer of surrounding passivation. Also shown in FIG. 20 a isvia 21′ that in this case has been created in about the center ofopening 15′. Via 21′ is more clearly shown in the cross section of FIG.20 b where also is shown interconnect line 23′ that now can be used toconnect the contact pad 17′ to additional electrical components orinterconnect networks. Interconnect line 23′ is in most instancesimbedded in a layer 25′ of dielectric that overlies a semiconductorsurface 10. This method of “vertical” interconnect need not be limitedto one interconnect via 21′ but can be extended to include a number ofvias, this is shown in top view in FIG. 20 c and in cross section inFIG. 20 d. The cross section that is shown in FIG. 20 d is taken alongthe line d-d′ of FIG. 20 c and shows three of the vias (one via 21′ andtwo vias 27′) that have been shown in top view in FIG. 20 c.Interconnect line 23′ in this case is used to establish electricalcontact between the contact pad 17′ and surrounding electricalcomponents (not shown). For most present day applications, tungsten isthe preferred metal that is used for the creation of metal vias 21′ and27′, the contact pad 17′ is preferably made using aluminum.

The above has been highlighted in some depth in order to establish thatthe invention starts after a contact has been created. This contact padmay be accessed in any of the methods that been highlighted above, anyprocessing that is provided by the invention therefore does not concernitself with the creation of vias to which the contact pad is connectedor with the creation of interconnect metal in the plane of the contactpad.

Processing steps that are required to implement the invention aredescribed next. FIGS. 6 through 13 b follow the processing sequence thatis required to create a metal bump in accordance with the top view andcross section that is shown in FIGS. 2 a through 3 d, that is no layerof polyimide is used for these processing steps.

FIG. 6 shows a cross section of substrate 10 on the surface of which acontact pad has been created, the following elements are highlighted:

-   -   10, a silicon substrate over the surface of which an aluminum        contact pad has been created    -   24, the aluminum contact pad    -   28, the probe mark or bump that has been created in surface of        the aluminum contact pad 24 by repetitive contacting of the        contact pad 24 by a tester probe (not shown)    -   29, a layer of dielectric that has been deposited over the        surface of substrate 10    -   32, a layer of passivation that has been deposited over the        surface of the layer 29 of dielectric. An opening has been        created in the layer 32 of passivation that aligns with the        aluminum contact pad 24, partially exposing the surface of the        contact pad 24.

FIG. 7 shows a cross section of the substrate 10 after the aluminumcontact pad 24 has partially etched in accordance with the opening 36 ofthe passivation 32. This etch of the aluminum pad has created opening 36in the aluminum pad 24 and has, as is the objective of the invention,removed the probe mark 28 and the regions surrounding the probe mark 28from the surface of the aluminum pad 24. The depth of the etch of thealuminum pad 24 can be controlled by controlling the etch time. Thisimplies that not all of the aluminum of contact pad 24 has to be removedfrom the surface of layer 29 of dielectric. As one of the preferredmethods of the invention that is shown in FIG. 7, a layer of aluminumwith a thickness of about 2000 Angstrom is left in place over thesurface of the layer 29 of dielectric, bounded by the opening 36 ofpassivation 32. From this it is clear that, where FIG. 7 shows a layer48 with a thickness of about 2000 Angstrom, this layer of aluminum maybe further removed from the surface of layer 29 of dielectric bycontinued etching of the contact pad 24, as shown in FIG. 9 a. It is ofinterest to note that contact pad 24 remains fully in place where thelayer 32 of passivation overlies the contact pad 24.

The etching of the aluminum pad 24 in accordance with opening 36 can, aspreviously stated, use methods of plasma enhanced dry etching or wetetching with a H₃PO₄ solution. Other methods for the etching of thealuminum pad have previously been highlighted and equally apply at thisstage in the process.

In order to obtain improved processing results and adhesion of UBM metalto the remaining aluminum contact pad 24 and to the exposed surface ofIMD layer 29, it is of value to perform an in-situ sputter clean of theexposed surfaces of the aluminum contact pad 24 and the layer 29 of IMD.This in-situ sputter clean is most beneficially performed before a layerof UBM is created.

To summarize FIGS. 7 through 9 b:

-   -   FIG. 7 shows a cross section where the contact pad has been        partially etched, stopping the etch of the aluminum pad 24 at        the point where about 2000 Angstrom of aluminum is left in        place; the contact pad is contacted by means of interconnect        metal (not shown) that is created in the plane of the contact        pad    -   FIG. 8 is identical to FIG. 7 except that for the case that is        shown in FIG. 8 the contact pad is contacted by means of vias 11    -   FIG. 9 a is identical with FIG. 7 except that the aluminum of        the contact pad 24 has been completely removed from above the        surface of layer 29 of dielectric in accordance with the opening        36 created in the layer 32 of passivation    -   FIG. 9 b is identical with FIG. 8 except that the aluminum of        the contact pad 24 has been completely removed from above the        surface of layer 29 of dielectric in accordance with the opening        36 created in the layer 32 of passivation.

The processing of the cross section that is shown in FIGS. 7 through 9 bcontinues as shown in cross section of FIG. 10 a. FIG. 10 a shows across section after the layer 33 of under bump metal (UBM) has beenblanket deposited over the surface of the wafer. Layer 33 of UBM can bedeposited by vacuum evaporation or by sputtering and may containmultiple layers of metal such as a layer of chrome, followed by a layerof copper. From the latter it is apparent that layer 33 of UBM maycomprise several layers of metal that are successively deposited.

For a UBM layer that is blanket deposited over the surface of the wafer,including the exposed surface of the contact pad 24 and the exposedsurface of layer 29 of dielectric (exposed in the opening 36), any ofthe conventional UBM materials can be used. A UBM layer can be depositedusing a sputter chamber or an Ion Metal Plasma (IMP) chamber, depositedat a temperature of between about 0 and 300 degrees C., a pressure ofbetween about 1 and 100 mTorr, using (for instance) copper or a copperalloy as the source (as highlighted above) at a flow rate of betweenabout 10 and 400 sccm and using argon as an ambient gas.

It must be emphasized with respect to the cross section that is shown inFIG. 10 a that layer 48 may have been completely removed by extendedetching of the contact pad 24, as previously indicated. This layer 48has been shown in FIG. 10 a as being etched down to about 2000 Angstrom,if this layer has been completely removed from above the layer 29 ofdielectric, the layer 33 of UBM is deposited directly on the surface oflayer 29 of dielectric.

FIG. 10 b shows a cross section after the layer 33 of under bump metal(UBM) has been deposited over the surface that is shown in cross sectionof FIG. 8, that is the embodiment of the invention where vias throughthe layer 29 of dielectric as used to make contact with contact pad 24.

FIG. 11 a is a continuation of FIG. 10 a and shows how a layer 39 ofphotoresist has been deposited over the layer 33 of UBM. Layer 39 ofphotoresist is patterned and developed, creating an opening 38 in thelayer 39 of photoresist that is slightly wider than the opening of thebonding pad of the to be created solder bump.

Next and also shown in cross section in FIG. 11 a, a layer 34 ofenhanced UBM, typically of copper or nickel and of a thickness betweenabout 1 and 10 μm is electroplated over the layer 33 of UBM. The UBMlayer 33 serves as the common electrode for the electroplating processwith the layer of photoresist still being in place.

It must again be pointed out with respect to the cross section that isshown in FIG. 11 a that layer 48, although this layer is shown in thiscross section, may in fact have been removed completely from the surfaceof the dielectric layer 29.

The cross section that is shown in FIG. 11 b will be recognized as acontinuation of the cross section shown in FIG. 10 b. The cross sectionof FIG. 11 b is created by applying processing steps (to the crosssection of FIG. 10 b) that are identical to the processing steps thathave been applied to create FIG. 11 a (from the cross section shown inFIG. 10 a). Where therefore FIG. 11 a is a continuation of FIG. 10 a,FIG. 11 b is a continuation of FIG. 10 b. All the remarks that have beenprovided relating to FIG. 11 a can also be made with respect to FIG. 11b, FIG. 11 b is shown since the vias are present in this cross section.

Next the layer 35 of bump metal (typically solder or gold) iselectroplated in contact with the layer 34 of enhanced UBM, this isshown in cross section in both FIG. 12 a (for the case where the contactpad is accessed by interconnect metal created in the plane of thecontact pad) and in FIG. 12 b (for the case where vias 11 have beenprovided through the underlying layer of dielectric). It must again bepointed out, with respect to both FIG. 12 a and FIG. 12 b, that layer48, although shown in cross section in these figures, may have beencompletely removed from the surface of layer 29 of dielectric.

The layer 35 of electroplated metal is centered in the opening 38 (FIGS.12 a and 12 b) that has been created in the layer 39 of photoresist.

FIGS. 13 a and 13 b show a cross section after the layer 39 (FIGS. 12 aand 12 b) of photoresist has been removed. The layer 33 of UBM has beenetched using the patterned layer 35 of electroplated metal as a mask.

The above summarized processing steps of electroplating that are usedfor the creation of a metal bump can be supplemented by the step ofcuring or pre-baking of the layers of photoresist after these layershave been deposited. The invention can also be applied to otherprocesses that are used to create solder bumps such as screen printingand stencil printing.

Where FIGS. 6 through 13 b have shown the metal bump of the inventionthat does not make use of a layer of polyimide, the following drawingsaddress the metal bump of the invention that does make use of a layer ofpolyimide. These drawings start with FIG. 14 a, it is assumed that priorto the cross section that is shown in FIG. 14 a the processing sequencethat has previously been discussed using FIGS. 6 through 9 b has beenperformed. In comparing FIG. 7 with FIG. 14 a and in comparing FIG. 8with FIG. 14 b, this latter statement can readily be accepted. Thedifference between FIG. 7 and FIG. 14 a is that a layer 50 of polyimidehas been deposited over the surface of the passivation layer 32. Layer50 has been patterned and etched, using conventional methods, creatingopening 36′ in the layer of polyimide. What must be remarked in thisrespect is that the diameter of opening 36′ can be slightly or evensignificantly smaller than the diameter of the opening 36 (FIG. 7) thathas been created in the layer 32 of passivation. The opening 36′ shouldcover the probe mark 28. The difference between FIG. 8 and FIG. 14 balso results from the deposition of a layer of polyimide over thesurface of the passivation layer 32 (FIG. 14 b). Layer 50 (FIG. 14 b)has been patterned and etched, using conventional methods, creatingopening 36′ in the layer of polyimide with a diameter of opening 36′that is slightly or significantly smaller than the diameter of theopening 36 (FIG. 8). The opening 36′ should cover the probe mark 28.

Some comments are in order at this time relating to the use of the layerof polyimide. The layer of polyimide is very important because thepolyimide covers fuses in order to prevent exposure of the fuses duringsubsequent etching of the damaged contact pads. The processing sequencefor SRAM wafers can be summarized as follows:

-   -   after SRAM wafers have been processed, a first chip probe test        (CP1) is performed    -   poorly performing memory bits are repaired by breaking the        related fuse    -   a second chip probe test (CP2) is performed    -   the surface of the whole wafer is covered with a layer of        polyimide    -   the deposited layer of polyimide is patterned, creating openings        to the contact pad, the aluminum pad is at this time partially        or completely removed by etching    -   after the previous step has been completed, regular solder bump        processing resumes.

FIG. 14 a can be compared with FIG. 7, a patterned layer 50 of polyimidehas been added to the cross section that is shown in FIG. 14 a.

FIG. 14 b can be compared with FIG. 8, a patterned layer 50 of polyimidehas been added to the cross section that is shown in FIG. 14 b.

FIG. 15 a can be compared with FIG. 10 a, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 15a.

FIG. 15 b can be compared with FIG. 10 b, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 15b.

FIG. 16 a can be compared with FIG. 11 a, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 16a.

FIG. 16 b can be compared with FIG. 11 b, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 16b.

FIG. 17 a can be compared with FIG. 12 a, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 17a.

FIG. 17 b can be compared with FIG. 12 b, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 17b.

FIG. 18 a can be compared with FIG. 13 a, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 18a.

FIG. 18 b can be compared with FIG. 13 b, a patterned layer 50 ofpolyimide has been added to the cross section that is shown in FIG. 18b.

From the cross section that is shown in FIG. 18 a, the cross sectionthat is shown in FIG. 4 b can be achieved by forming the metal bump 35by reflowing the metal bump layer 35 that is shown in FIG. 18 a.

From the cross section that is shown in FIG. 18 b, the cross sectionthat is shown in FIG. 5 b can be achieved by forming the metal bump 35by reflowing the metal bump layer 35 that is shown in FIG. 18 b.

To review and summarize the invention:

-   -   the invention starts with a semiconductor surface, a layer of        dielectric has been deposited over the semiconductor surface, a        contact pad has been provided on the layer of dielectric, the        contact pad has served as an Input/Output (I/O) point of contact        during semiconductor device testing, the contact pad is assumed        to be connected to at least one point of electrical contact        provided in or on the surface of the substrate, the at least one        point of electrical contact is assumed to be connected to at        least one semiconductor device having been provided in or on the        surface of the substrate, the contact pad having an exposed        surface    -   a layer of passivation is deposited over a semiconductor surface        including the surface of said contact pad    -   the layer of passivation is patterned and etched, creating an        opening in the layer of passivation having a first diameter,        partially exposing the surface of the contact pad over a surface        area of the first diameter, the opening in the layer of        passivation being centered with respect to the contact pad    -   the contact pad is completely or partially etched in accordance        with the opening created in the passivation layer, either        leaving a thin layer of aluminum in place or partially exposing        the surface of the layer of dielectric deposited over the        surface of the substrate    -   an in-situ sputter clean is performed of the exposed surface of        the contact pad    -   a layer of Under Bump Metallurgy (UBM) is sputtered over the        surface of the layer of passivation, including the exposed        surfaces of the contact pad    -   a layer of photoresist is deposited over the semiconductor        surface of the layer of UBM    -   the layer of photoresist is patterned and etched, creating an        opening in the layer of photoresist that is aligned with the        contact pad, partially exposing the surface of the layer of UBM    -   the exposed surface of the layer of UBM is electroplated with a        layer of enhanced UBM    -   the layer of enhanced UBM is electroplated with a thick layer of        bump metal, partially filling the opening created in the layer        of photoresist    -   the patterned and etched layer of photoresist is removed from        above the semiconductor surface    -   the layer of UBM is etched using the deposited layer of bump        metal as a mask, and    -   the surface of said layer of bump metal is reflowed, forming the        metal bump.

In addition, a layer of polyimide may be deposited over the layer ofpassivation, patterned and etched, creating an opening in the layer ofpolyimide that has a diameter which is slightly or significantly smallerthan the diameter of the opening created in the layer of passivation.The created opening is larger than the size of the probe mark.Processing, after the opening has been created in the layer ofpolyimide, is the same as the processing that is performed (without thelayer of polyimide) after an opening has been created in the layer ofpassivation.

Although the invention has been described and illustrated with referenceto specific illustrative embodiments thereof, it is not intended thatthe invention be limited to those illustrative embodiments. Thoseskilled in the art will recognize that variations and modifications canbe made without departing from the spirit of the invention. It istherefore intended to include within the invention all such variationsand modifications which fall within the scope of the appended claims andequivalents thereof.

1. A method for forming a metal bump on a semiconductor substrate,comprising the steps of: providing a semiconductor substrate, saidsemiconductor substrate having been provided in or on the surfacethereof with a contact pad, said contact pad sitting on an underlyinglayer of dielectric and being in electrical contact with at least onepoint of electrical contact in or on the surface of said substrate;depositing a layer of passivation over the surface of said layer ofdielectric underlying the contact pad, including the surface of saidcontact pad; patterning and etching said layer of passivation, creatingan opening in said layer of passivation having a first diameter,partially exposing the surface of said contact pad over a surface areaof said first diameter, said first diameter of said opening created insaid layer of passivation being smaller than a surface area of saidcontact pad by a measurable amount; etching said contact pad, using saidlayer of passivation as a mask, partially or completely first removingsaid contact pad from above the surface of said layer of dielectric,creating a opening in said contact pad having a diameter being aboutequal to said first diameter; sputtering a layer of Under BumpMetallurgy (UBM) over the surface of said layer of passivation,including said opening created in said contact pad; depositing andpatterning a layer of photoresist, creating an opening in thephotoresist with a slightly larger dimension than said first diameter;electroplating a layer of bump metal in the photoresist opening;stripping the layer of photoresist and etching said layer of UBM, usingsaid layer of bump metal as a mask; and reflowing the surface of saidlayer of bump metal, forming the metal bump. 2-40. (canceled)
 41. Asemiconductor device comprising: a semiconductor substrate; a contactpad overlying said semiconductor substrate with a dielectric layertherebetween; a passivation layer overlying said dielectric layer andthe periphery of said contact pad wherein said passivation layer is notphotoresist and wherein a first opening is made completely through saidpassivation layer and at least partially through said contact pad; a UBMlayer overlying said contact pad; a bump metal overlying said UBM layerwherein said bump metal and said UBM layer are defined as slightlylarger than said second opening in said passivation layer and whereinsaid UBM layer is formed into a bump.
 42. The device of claim 1 whereinsaid first opening is not entirely through said contact pad.
 43. Thedevice of claim 1 wherein said opening created in said first opening isentirely through said contact pad.
 44. The device of claim 1 whereinsaid contact pad comprises aluminum or copper or a compound thereof. 45.The device of claim 1 wherein said UBM layer is formed byelectroplating.
 46. The device of claim 1 further comprising aninterconnect metal level that electrically connects to said contact padwherein said interconnect metal level is in the same plane as saidcontact pad.
 47. The device of claim 1 further comprising aninterconnect metal level that electrically connects to said contact padwherein said interconnect metal level underlies said contact pad and isconnected through a via.